1. Technical Field
The present invention relates to touch input devices. In particular, to opto-matrix frames having a minimum component count.
2. Background Art
Historically, keyboards were used to interact with display devices. Due to the needs of particular users, a number of alternative methods of interacting with display devices were developed. Included in the alternatives were items such as mice, light pens, tablets, joysticks, and the like. All of these methods have the disadvantage of requiring hardware extraneous to the display. The development of touch panel displays provided an alternative method of interacting with a display device which has the additional advantage of not requiring hardware extraneous to the displays touch panel displays allow a user to interact by first presenting information on the screen. Then the user interacts by touching the screen at locations based on information displayed on the screen. The touch panel senses the location of the finger or stylus and communicates that information to the computer.
There are known alternative methods of designing touch panel displays. One method uses a transparent membrane switch which covers the surface of the display screen. Over time, the membrane design creates vision problems for the user. This is because the membrane lies directly over the screen. Therefore, membrane wear will have a direct effect on how well a user can see the display. A preferable method is the opto-matrix display. This type of touch panel display places nothing on the surface of the screen, eliminating the problems caused by membrane wear. Further, the frequency of energy used can be selected so that it is outside of the visible light range, thereby rendering the matrix invisible to the user.
However, a disadvantage associated with opto-matrix touch panel displays is the high component count and consequent high manufacturing expense. For example, a large number of light emitting diodes (emitters) are required to create the optical matrix. A correspondingly large number of detectors paired with corresponding emitters, are required to detect light, or its absence, in the matrix. Further, scanning the emitters and monitoring the detectors typically requires significant on-board processing capability to scan the emitter/detector pairs, measure the difference between detector output before and after the emitter is turned on, and determine if a stylus is present at a given location. Touch panel displays also include digital to analog converters to allow data to be converted prior to being transferred to computers. Due to the difference in strength of emitter signals and the difference in sensitivity of detector output, errors can arise in the form of false stylus detection or failure to detect a stylus when present. Addressing the problems created by the difference in emitter/ detector signals results in additional hardware.
Some attempts have been made to reduce the number of emitters and detectors required for the optical matrix in the display. For example, U.S. Pat. No. 4,733,068 to Sherbeck discloses a method of reducing the number of emitters by placing emitters in the corners of the bezel with a plurality of detectors on opposing sides of the bezel. This approach allows the number of emitters to be reduced, but at the same time prevents any reduction in the number of detectors. Likewise, U.S. Pat. No. 4,766,424 to Adler et al uses a similar approach by attaching a diode connected to a light conducting strip to two sides of the bezel and exciting them with a plurality of emitters on the other two sides of the bezel. This approach allows the number of detectors to be reduced but prevents any reduction in the number of emitters. As a result, while attempts to reduce the number of emitters and detectors have been successful, the very solutions to the problem of reducing the number of emitters prevents reduction in the number of detectors, and the solution to the problem of reducing the number of detector has prevented the reduction of both emitters. Therefore, the prior art has not shown the ability to reduce the number of emitters and detectors at the same time.
The prior art has failed to provide touch panel input device that not only has the known advantages of opto-matrix displays, such as the absence of extraneous hardware, and the superior visual qualities of opto-matrix touch panels over membrane touch panel input devices, but one which also overcomes the disadvantages of known opto-matrix touch panel devices, which results in high cost primarily due to the number of components required to implement such a device and in particular due to the large number of emitters and detectors required to operate an optical touch panel display, and the additional circuitry required to correct differences in signal strength of emitters and detectors.